This invention relates to charging flowable materials into selected cells of a honeycomb structure and, more particularly, to a method and related apparatus for selectively manifolding (i.e. plugging) cells of a honeycomb structure for the fabrication of filter bodies and other manifolded honeycomb structures.
Honeycomb structures having transverse cross-sectional cellular densities of one to several hundred cells per square inch, especially when formed from ceramic materials, have several uses, including solid particulate filter bodies and stationary heat exchangers, which require selected cells of the structure to be sealed by manifolding or other means at one or both of their ends. The term "seal" and its corresponding grammatical and derivative forms (i.e. "sealed", "sealant", "sealing", etc.) are used herein to refer to both porous and non-porous closing and means of closing the open transverse cross-sectional areas of the cells of honeycomb structures.
It is well known that a solid particulate filter body may be fabricated utilizing a honeycomb structure formed by a matrix of intersecting, thin, porous walls which extend across and between two of its opposing end faces and form a large number of adjoining hollow passages, channels or cells which also extend between and are open at the end faces of the structure. To form a filter, one end of each of the cells is sealed, a first subset of cells being sealed at one end face and the remaining cells being sealed at the remaining opposing end face of the structure. The contamination fluid is brought under pressure to one face ("inlet" face) and enters the filter bodies via the cells which are open at the inlet face ("inlet" cells). Because the inlet cells are sealed at the remaining ("outlet") end face of the body, the contaminated fluid is forced through the thin, porous walls into adjoining cells which are sealed at the inlet face and open at the outlet end face of the filter body ("outlet" cells). The solid particulate contaminant in the fluid which is too large to pass through the porous openings in the walls is left behind and a now cleansed fluid exits the filter body through the outlet cells for use.
Rodney Frost and Irwin Lachman describe and claim in a copending application Ser. No. 165,646, filed July 3, 1980 and entitled FILTER AND RELATED APPARATUS, a most efficient solid particulate filter body formed from a honeycomb structure in which the cells are provided in transverse, cross-sectional densities between approximately one and one hundred cells per square centimeter with transverse, cross-sectional geometries having no internal angles less than thirty degrees, such as squares, rectangles, equilateral and certain other triangles, circles, certain elipses, etc. The cells are also arranged in mutually parallel rows and/or columns. Alternate cells at one end face are filled in a checkered or checkerboard pattern and the remaining alternate cells are sealed at the remaining end face of the structure in a reversed pattern. Thus formed, either end face of the filter body may be used as its inlet or outlet face and each inlet cell shares common walls with only adjoining outlet cells, and vice versa. Other cellular cross-sectional geometries and other patterns of sealed cells may be employed to fabricate effective, although perhaps less efficient filter bodies than those of Frost and Lachman.
For the mass production of such filters, it is highly desirable to be able to seal selected cell ends as rapidly and as inexpensively as possible. Frost and Lachman in the previously referred to application Ser. No. 165,646 describe fabricating filter bodies by plugging the end of each cell individually with a hand-held, single nozzle, air actuated sealing gun. The hand plugging of individual cells by this process is long and tedious and is not suited for the commercial production of such filters and other manifolded honeycomb structures which may have thousands of cells to be selectively sealed. Frost and Lachman also postulate the use of an array of sealant nozzles so that the sealing mixture may be simultaneously injected into a plurality or all of the alternate cells at each end face of the honeycomb structure. However, a working model of this device is not known to exist for plugging honeycomb structures having the higher cell densities referred to.
An alternative approach to manifolding selected cells at an end face of a honeycomb structure is described and claimed by Rodney Frost and Robert Paisley in another pending application Ser. No. 283,733, filed on July 15, 1981 and entitled METHOD AND APPARATUS FOR SELECTIVELY CHARGING HONEYCOMB STRUCTURES, in which an open surface of a honeycomb structure is covered by a mask having a number of openings extending through it. Sealing material is charged against the outer surface of the mask and through its openings into the proximal open ends of cells opposite the openings. Frost and Paisley specifically describe the use of a rigid plate having a plurality of bores extending through it which are spaced and sized to coincide with the open ends of the selected cells at the end face of a honeycomb structure when the plate is positioned against the end face and aligned with its bores over selected cells. Successful use of such an apparatus is dependant upon the ability to provide honeycomb structures having end faces conforming to the face of the covering apparatus so as to prevent gaps therebetween which would allow the sealing material to charge into adjoining cells and to provide predetermined, undistorted positioning of the cells at the end face of the honeycomb structure for accurate registration of the selected cells with the openings in the mask, again, to prevent possible charging of sealing material into adjoining cells.
Masks have also been formed for manifolding cells which are regularly interspersed among essentially mutually parallel rows and essentially mutually parallel columns at an open surface of a honeycomb structure by applying strips of an adhesive backed flexible webbing impermeable to the sealing material, such as masking tape, over selected rows and columns of cells or, alternatively, by providing a matrix of spaced, overlayed strips of a resilient, impermeable and reusable material such as metal foil which are joined together and fitted with or without an underlying gasket, over the open surface of the structure with openings through the matrix and gasket, if provided, aligned over the cells to be charged. By providing a honeycomb structure with cells arranged in mutually parallel rows and mutually parallel columns and covering alternate rows and alternate columns of cells with strips of a suitable flexible material such as the masking tape or the joined thin metal strips, the open ends of one-half of a subset of cells arranged in a checkered pattern across the end face were exposed. After filling the ends of these cells, the strips were removed and strips applied covering the remaining alternate rows and remaining alternate columns thereby exposing the open ends of the remaining half of the subset of cells of the checkered pattern at the end face for filling. Both embodiments provide greater flexibility in dealing with surface height variations and better sealing of the cell ends including those which may be damaged than does the rigid plate embodiment. However, both embodiments must be applied twice to each end face to manifold the alternate cells in the desired checkered pattern of Frost and Lachman. This is a significant limitation with respect to the tape strips which must be individually applied across each end face, a time consuming task. The reusable matrix and gasket of the second embodiment may be more quickly applied and removed, but like the rigid plate embodiments, cannot be adapted to distortions in the cell locations at the end faces.
Noll, et al in U.S. Pat. No. 4,041,591, describe alternate methods of fabricating a multiple flow path body such as a stationary heat exchanger in which a honeycomb structure is provided having its cells arranged in columns across its open end faces, an open end face of a honeycomb structure is dipped into a flowable resist material and the resist material removed from selected columns by cutting it away together with the common walls of the adjoining cells in the selected column or, alternatively, the walls between the adjoining cells of the selected columns are cut away at the open end face of the structure before dipping the end face into the flowable resist material, then the resist material is blown from the selected columns using compressed air directed down the selected columns where the adjoining cell walls have been removed. The end face was thereafter dipped into a slurry of cement to form a sealed channel across each of the selected columns. The remaining flowable resist material was subsequently removed by heating. As the cross-sectional density of cells in the honeycomb structure is increased, for example to improve the efficiency of a filter body, the tolerances needed for the removal of adjoining cells walls required by the Noll, et al method tighten. The problem is particularly heightened when the filter bodies are fabricated from extruded ceramic or ceramic based honeycomb structures as the present state of the ceramic extrusion art cannot provide perfectly parallel rows and/or columns of cells. Also, the Noll, et al method requires the partial destruction of adjoining cell walls and is entirely unsuited for the fabrication of filter bodies where the cells are sealed in a checkered and other possible alternating cell patterns at the end faces.